In many optical designs, solid-glass optical components are used to provide redirection of optical imaging therethrough. However, the use of solid-glass optical components may introduce a large amount of weight into a design, rendering the design unusable. For example, various optical systems are used in conjunction with headgear of aviation navigators. Such optical systems may include combiner elements. The combiner elements may be prismatic with two parallel flat surfaces for internal reflection of light therethrough. In many high performance optical systems, combiners require high quality aspheric surfaces to improve the performance of such systems and correct for distortion of image rays and wavefronts in the system. However, high-quality aspheric surfaces are very expensive to produce, requiring the services of highly skilled personnel. Thus, an optical system constructed of glass components may result in headgear that is too heavy to serve its intended purpose and be cost prohibitive.
As is known to one skilled in the art, the use of plastic to produce light weight elements can solve the problem associated with the weight of glass components. The surfaces of such plastic components can be machined to many geometric shapes, including aspheric surfaces. One method of such machining is the use of diamond turning as described in U.S. Pat. No. 4,852,436 to Benjamin or as is generally known to one skilled in the art. Such diamond turning produces a substantially symmetrical surface about a center point of the asphere.
The machining of surfaces on plastic optical elements is difficult because of the softness and other physical characteristics of the material. Such machining, such as diamond turning, does not produce a completely smooth surface. The diamond turning, for example, produces an aspheric surface on a plastic optical element which has many radial ridges on the aspheric surface symmetric about the center point. In high performance systems, such ridges produced by the diamond turning can create a haze from diffraction or light scattering due to the microscopic defects or ridges as light passes through the optical element.
In addition, because the diamond turning creates a surface which is symmetric about a center of an aspherical surface designed to correct for distortion of image rays, a certain degree of astigmatism may be created by such aspherical shape. Such haze and astigmatism is unacceptable when the optical element is used in vision type systems. Therefore, there exists a need to reduce the effect of such problems associated with the diamond turned plastic asphere surfaces.